The Word for World is Forest (Hainish Cycle, #5)

by Ursula K. Le Guin

A realist is a man who knows both the world and his own dreams. You’re not sane: there’s not one man in a thousand of you who knows how to dream. Not even Lyubov and he was the best among you. You sleep, you wake and forget your dreams, you sleep again and wake again, and so you spend your whole lives, and you think that is being, life, reality! You are not children, you are grown men, but insane. And that’s why we had to kill you, before you drove us mad.